Rolling-element bearing systems have been used in the engineering world for many years. In their basic configuration, such bearing systems are characterized by an outer ring and an inner ring with the rolling elements positioned therebetween. These rings are often called races in that both the outer and inner rings have "raceways" in which the rolling elements move. A retainer ring placed between individual rolling elements to maintain the proper spacing between them may also be included. The rolling elements can be one of many types including ball, roller, tapered roller, spherical roller, etc.
As a general rule, bearing systems are sold in assemblies. These assemblies include the races, the retainer ring and the rolling elements arranged in a pre-assembled fashion. Once the design requirements of the rotating shaft are understood (i.e. the radial force, the axial force, the RPM, service life, etc.), the type of bearing element can be chosen. Once the bearing element is determined, the type and size of the assembly is known. The last aspect of the design process is to design the mounting structure in which the bearing assembly will be retained. It is this last aspect of the design process where the present invention is particularly useful.
Retaining the bearing assembly in the bearing mounting structure requires a retention force in a predetermined range. If the retention force is too small, the bearing assembly may slip or become completely dislodged within the bearing mounting structure. Alternatively, if the retention force is too large, then the bearing elements will gall the raceways ultimately leading to premature failure. Because of these potential failure modes, all components of the bearing assembly must be manufactured with extremely tight tolerances. Furthermore, the bearing mounting structure must provide for a cavity with a tight tolerance in its diametric dimension to properly accommodate the bearing assembly.
For example, in a machine running at 700 RPM with 50 pound-force (lbf) of radial force and 200 lbf of axial force, a ball-type of bearing element can be used which dictates a bearing assembly having a 2.4406 inch diameter on the exterior surface of the outer race with a +0.0003 and -0.0002 inch tolerance. The internal cavity of the bearing mounting structure in which the bearing assembly resides has a diameter of 2.440 inch with a tolerance of +0.000 inch and -0.001 inch. The diameter of the internal cavity must be within 0.001 inch (one mil) for the bearing assembly to be properly installed. If each bearing mounting structure is machined, then achieving this level of tolerance is feasible. However, machining to these tight tolerances is extremely expensive. When the bearing mounting structures are mass produced, other low-cost processes such as stamping or drawing are used to reduce cost. Since these low-cost processes are not amenable to controlling tight tolerances, many finished products are out of tolerance and discarded as waste or scrap.
One resolution to this problem has been the utilization of tolerance rings. A tolerance ring is a shim-like device which is placed into the cavity of a bearing mounting structure to assist in achieving the proper retention force. However, this additional part adds cost to the bearing system. Moreover, the labor and processes needed to install such a ring also increase the cost of the final product.
Therefore, a need exists for a bearing mounting structure that allows the tolerances to be loosened when using typical low-cost, metal-forming processes such as stamping or drawing.